Filter cassette article, and filter comprising same

ABSTRACT

A filtration cassette including a multilaminate array of sheets including filter sheets alternating with permeate sheet members and retentate sheet members, and a cross-flow filter device comprising a multiplicity of stacked filtration cassettes of such type. The improvements associated with the filtration cassettes described herein include, but are not limited to, at least one of: reinforced inlet(s) providing for longevity and improved cleanability of the cassettes; spacer permeate screens to limit throughput restriction; stainless steel or otherwise stiffened permeate sheets to prevent movement and increase flux; and stainless steel permeate sheets that can be used with ultrasonic transmission to minimize fouling of the filter sheets and extend cleaning cycles. Advantageously, the filtration cassettes are more resistant to higher temperatures than the filtration cassettes of the prior art.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to co-pending U.S. ProvisionalApplication No. 62/658,787 filed on Apr. 17, 2018, the contents of whichare incorporated by reference herein for all purposes.

FIELD

The present invention relates generally to improved filtrationcassettes, comprising filter sheets arranged in a multilaminate,peripherally bonded array wherein the filter sheets alternate with atleast one foraminous (e.g., screen or mesh) permeate sheet element, andretentate channel elements. The improvements associated with thefiltration cassettes described herein include, but are not limited to,at least one of: reinforced inlet(s) providing for longevity andimproved cleanability of the cassettes; spacer permeate screens to limitthroughput restriction; stainless steel or otherwise stiffened permeatesheets to prevent movement and increase flux; and stainless steelpermeate sheets that can be used with ultrasonic transmission tominimize fouling of the permeate sheet and extend cleaning cycles.

BACKGROUND

Stacked plate cross-flow filters are utilized in a variety ofsolids-liquid or liquid-liquid separation operations, including thedewatering of solids-liquid suspensions such as aqueous biomasssuspensions, the desalting of proteins, and the removal of secretedmetabolites from cellular cultures. In such systems, the stacked platesmaking up the cross-flow filter are typically mounted in a framestructure whereby the respective plates are retained in alignment withone another, in a so-called “plate and frame” construction.

The plate and frame filter typically utilizes a liquid source materialconduit extending through the stacked plates as a means to introduceliquid source material into the flow channels defined between adjacentplates in the stacked plate assembly. The flow channels in the plate andframe filter contain filter elements, such as disposable filter papersheets or polymeric membranes, with which the liquid source material iscontacted and through which a permeate passes. A withdrawal conduitcorrespondingly extends through the stacked plates, in liquid flowcommunication with the respective flow channels of the stacked plateassembly, and conveys a retentate out of the filter system. A permeateconduit is also provided to withdraw permeate out of the stacked plateassembly.

As filtration proceeds in the plate and frame filters of the prior art,the solids become more concentrated in the flow channels of the filter,on the “liquid source material sides,” i.e., active filtration surfacesin the open area between the adjacent filter sheets, until the desiredconcentration has been achieved and the desired volume processed oruntil the flux has decayed to the point that cleaning is justified. Thefilter is then harvested for solids and liquids and then drained priorto being cleaned in place (CIP), or alternatively, it may be fully shutdown after a predetermined time or after a predetermined level of solidshas accumulated in the flow channels between the filtration surfaces ofthe filter sheets, following which the system is drained of liquid andthen cleaned in place (CIP).

Applicant's filter plate as disclosed in prior U.S. Pat. No. 5,593,580is efficient in effecting mass transfer operations, e.g., dewatering ofaqueous biomass suspensions, desalting of proteins, and removal ofsecreted metabolites from cellular suspensions. Such filter plate, shownin FIG. 1, is of a type comprising filter sheets arranged in amultilaminate, peripherally bonded array, wherein the filter sheetelements (20) alternate with foraminous (e.g., screen or mesh) permeatesheet elements (30), and ribbed retentate channel elements (10). Each ofsheets is generally co-extensive in areal extent with the others, andwhen consolidated into a cassette article, the fluid inlet cutoutopening (9) and the fluid outlet cutout opening (12) and open retentateflow channels (8) in each of the respective sheet elements are inregistration.

The principal feature of the portion of the prior art assembly shown inFIG. 1 is to enable uniform retentate flow via transversely-located openretentate flow channels (8) that are identical in length and create aneven path length within the filter module from the inlet of the moduleto the outlet of the module as shown in FIG. 2. Uniform retentate flowin an open channel (8) greatly improves the consistency of separation aswell as the ability to clean the filter plate.

While applicant's prior art filter modules function well within theirdesign limits, the market still demands alternative filter modules thatcan be utilized under different, and often more extreme, conditions. Theimprovements described herein enable tolerance for higher cross flowrates per unit area, higher particulate loadings, and improvedresistance to back pressure. In the filter modules of the prior art,when the velocity and/or viscosity of the liquid source material orretentate is increased beyond a predefined limit, several effects canarise. For example, some of the entrances to the retentate flow channels(8) may cease to remain stiff and parallel to the adjacent retentateflow channel (see, e.g., FIG. 3A relative to FIG. 3B). This occurs whensheet material at the fluid inlet openings (9) bends or folds and thusblocks the entrance to an adjacent retentate flow channel (8), therebyincreasing the flow rate to the remaining unobstructed channels. Thiscan result in a cascading effect whereby the same recirculating crossflow rate is continuously being presented to an ever-decreasing numberof pathways (i.e., retentate flow channels). Resultantly, the flux ratereduces as decreasing filter sheet surface area is available to therecirculating fluid. Further, the obstructed retentate channels becomedifficult to clean.

A similar effect occurs within the length of the retentate flow channelof the prior art when operated beyond its design limit. As the pressuredrop down the retentate flow channel increases, the “stiffness” of aparticular channel's support (i.e., first filter sheet (20), permeatesheet (30), second filter sheet (20) spanning the cross section of theretentate channel) may be distended, especially when the liquid sourcematerial or retentate has a very high viscosity and/or a very highsolids content. As a result, the distended channel begins to encroachinto the adjacent retentate flow channel, which can partially collapse.This triggers the cascade effect described above whereby the flux ratedecreases, the recirculating velocity decreases in the affected channeland the suspended solids may aggregate and solidify in the affectedchannel thus rendering the filter module hard or impossible to clean.

Accordingly, alternative filtration cassettes of a type which provideimproved mass transfer efficiency and utility relative to the filtercassettes of the prior art are described herein. The alternativefiltration cassettes maximize the flux rate through the filter cassette,as well as efficiency of cleaning. Further, the alternative filtrationcassettes are more resistant to higher temperatures than the filtrationcassettes of the prior art.

SUMMARY

The present invention relates to an alternative filtration module thatcan be utilized under different, and often more extreme, conditions.

In one aspect, a filtration cassette is described, said filtrationcassette comprising at least one assembly, wherein the at least oneassembly comprises:

-   -   a multilaminate array of sheet members of generally rectangular        and generally planar shape, each sheet having a first end and a        second end longitudinally opposite the first end and a        thickness, wherein the sheet members comprise in sequence in        said array a first retentate sheet, (a first filter sheet, a        permeate sheet, a second filter sheet, and a second retentate        sheet)_(n), wherein each of the first filter sheet, the permeate        sheet, and the second filter sheet members in said array have at        least one fluid opening at the first end thereof, and at least        one fluid opening at the second end thereof, wherein the first        end fluid opening(s) of the array are in register with one        another and the second end fluid opening(s) of the array are in        register with one another, and wherein n=1, 2, 3, 4, 5, 6, 7, 8,        9, 10, or more, wherein the first and second retentate sheets        have at least one channel opening therein, each channel opening        extending longitudinally between the first end fluid opening(s)        and the second end fluid opening(s) in the array and wherein the        at least one channel opening is open through the entire        thickness of the first and second retentate sheets to permit a        fluid to contact the adjacent filter sheets, and wherein the        first and second retentate sheets are bonded to the adjacent        filter sheets about peripheral end and side portions thereof;        and    -   two assembly end plates sandwiching the multilaminate array of        sheets, wherein the two assembly end plates comprise at least        one fluid opening at the first end thereof, and at least one        fluid opening at the second end thereof, or both, in register        with the fluid openings of the array,    -   wherein the at least one assembly further comprises at least one        permeate passage opening at longitudinal side margin portions of        the assembly(s),        wherein the filter cassette further comprises at least one of        options (I), (II), (III), or (IV), or any combination of        (I)-(IV):    -   (I) a cap positioned on at least a portion of the first end        fluid opening(s) or at least a portion of the second end fluid        opening(s), or both, of a permeate pack, wherein the permeate        pack comprises the first filter sheet, the permeate sheet, and        the second filter sheet members, wherein the cap is positioned        proximate to the channel openings of the first and second        retentate sheets;    -   (II) the fluid openings at the first end, the fluid openings at        the second end, or both the fluid openings at the first and        second end, are cut as an irregular pentagon having a “V”        positioned proximate to the channel openings of the first and        second retentate sheets;    -   (III) a first permeate screen spacer positioned between the        first filter sheet and the permeate sheet or a second permeate        screen spacer positioned between the second filter sheet and the        permeate sheet, or both, wherein the permeate screen spacer(s)        comprise fluid openings in register with the fluid openings of        the array;    -   (IV) the permeate sheet comprises a metal matrix or other        reinforced porous material of requisite thickness.

In another aspect, a method of separating a target substance from aliquid source material is described, said method comprising:

flowing the liquid source material into at least one filtration cassetteso as to recover a permeate fluid for disposal, reuse, furtherfiltration, or as a target product; and

recovering a retentate stream for disposal, reuse, further filtration,or as a target product, wherein the at least one filtration cassettecomprise at least one assembly, wherein the at least one assemblycomprises:

-   -   a multilaminate array of sheet members of generally rectangular        and generally planar shape, each sheet having a first end and a        second end longitudinally opposite the first end and a        thickness, wherein the sheet members comprise in sequence in        said array a first retentate sheet, (a first filter sheet, a        permeate sheet, a second filter sheet, and a second retentate        sheet)_(n), wherein each of the first filter sheet, the permeate        sheet, and the second filter sheet members in said array have at        least one fluid opening at the first end thereof, and at least        one fluid opening at the second end thereof, wherein the first        end fluid opening(s) of the array are in register with one        another and the second end fluid opening(s) of the array are in        register with one another, and wherein n=1, 2, 3, 4, 5, 6, 7, 8,        9, 10, or more, wherein the first and second retentate sheets        have at least one channel opening therein, each channel opening        extending longitudinally between the first end fluid opening(s)        and the second end fluid opening(s) in the array and wherein the        at least one channel opening is open through the entire        thickness of the first and second retentate sheets to permit a        fluid to contact the adjacent filter sheets, and wherein the        first and second retentate sheets are bonded to the adjacent        filter sheets about peripheral end and side portions thereof;        and    -   two assembly end plates sandwiching the multilaminate array of        sheets, wherein the two assembly end plates comprise at least        one fluid opening at the first end thereof, and at least one        fluid opening at the second end thereof, or both, in register        with the fluid openings of the array,    -   wherein the at least one assembly further comprises at least one        permeate passage opening at longitudinal side margin portions of        the assembly(s),        wherein the filter cassette further comprises at least one of        options (I), (II), (III), or (IV), or any combination of        (I)-(IV):    -   (I) a cap positioned on at least a portion of the first end        fluid opening(s) or at least a portion of the second end fluid        opening(s), or both, of a permeate pack, wherein the permeate        pack comprises the first filter sheet, the permeate sheet, and        the second filter sheet members, wherein the cap is positioned        proximate to the channel openings of the first and second        retentate sheets;    -   (II) the fluid openings at the first end, the fluid openings at        the second end, or both the fluid openings at the first and        second end, are cut as an irregular pentagon having a “V”        positioned proximate to the channel openings of the first and        second retentate sheets;    -   (III) a first permeate screen spacer positioned between the        first filter sheet and the permeate sheet or a second permeate        screen spacer positioned between the second filter sheet and the        permeate sheet, or both, wherein the permeate screen spacer(s)        comprise fluid openings in register with the fluid openings of        the array;    -   (IV) the permeate sheet comprises a metal matrix or other        reinforced porous material of requisite thickness.

Other aspects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of the assembly of sheets in a cross-flowfiltration cassette of the prior art, wherein the assembly end platesare not shown.

FIG. 2 illustrates the flow pattern of the fluid through an assembly ofsheets between holder plates with transversely located first end fluidand second end fluid openings, a permeate outlet, and an optionalpermeate inlet.

FIG. 3A is a picture of an assembly of an unused filter cassette of theprior art, showing the stiff and parallel retentate channel entrances.

FIG. 3B is a picture of an assembly of a used filter cassette of theprior art nearing the end of its utility, showing blocked retentatechannel entrances and a lack of parallelism to the adjacent channel.

FIG. 4A is a top plan view of a permeate pack having capped (22) fluidopenings (9) and an indication of a cross-section along A-A′.

FIG. 4B illustrates alternative cap (22) shapes.

FIG. 4C illustrates a generic “U-shaped” cap.

FIG. 4D illustrates an alternative filter sheet (20) having “notched”fluid openings (9), which are stiffer than the traditional square orrectangular cut-out openings.

FIG. 4E is a close-up of the notched cut-out openings of FIG. 4D.

FIG. 5A is a perspective view of FIG. 4A showing a first filter sheet(20), a permeate sheet (30), and a second filter sheet (20) havingcapped (22) fluid openings (9).

FIG. 5B is a cross-sectional view of FIG. 4A along A-A′ showing theinstalled cap (22).

FIG. 5C is a picture of an assembly of the filter cassette of thepresent invention with the installed caps.

FIG. 5D is a perspective view of the assembly of the present invention,including the installed caps, wherein the assembly end plates are notshown.

FIG. 6A is a picture of an assembly of a used filter cassette with theinstalled caps before cleaning.

FIG. 6B is a picture of an assembly of the used filter cassette with theinstalled caps after cleaning.

FIG. 7A is a cross section of the first filter sheet (20), the permeatesheet (30), and the second filter sheet (20) of the prior art.

FIG. 7B is a picture of flow channels of a permeate sheet (30) betweentwo filter sheets.

FIG. 8 is a cross section of the first filter sheet (20), the firstpermeate screen spacer (40), the permeate sheet (30), the secondpermeate screen spacer (40), and the second filter sheet (20) describedherein.

FIG. 9A is a photo of an embodiment of the filter sheet (20), anembodiment of the permeate screen spacer (40), and an embodiment of thepermeate sheet (30) as described herein.

FIG. 9B is a photo of a permeate screen spacer between a permeate sheetand a filter sheet.

FIG. 10A is an embodiment of the pattern of the permeate screen spacer.

FIG. 10B is another embodiment of the pattern of the permeate screenspacer.

FIG. 10C is another embodiment of the pattern of the permeate screenspacer.

FIG. 10D is another embodiment of the pattern of the permeate screenspacer.

FIG. 11 is a perspective view of the assembly of the present invention,including the installed caps (22) and the permeate screen spacers (40),wherein the assembly end plates are not shown.

FIG. 12 is a photo of a stainless steel permeate sheet.

FIG. 13A illustrates an example of parallel flow pattern of the fluidthrough a module or cassette.

FIG. 13B illustrates an example of series flow pattern of the fluidthrough a module or cassette.

FIG. 14A is a perspective view of an alternative embodiment of the capincluding clips.

FIG. 14B is a side view of the cap of FIG. 14A.

FIG. 14C is a perspective view of another alternative embodiment of thecap including clips, wherein the cap is not folded.

FIG. 14D is a side view of the cap of FIG. 14C, illustrating anembodiment of the clips.

FIG. 14E is a perspective view of another alternative embodiment of thecap including “hooks.”

FIG. 14F is a side view of the cap of FIG. 14E, illustrating anembodiment of the “hook.”

FIG. 14G is a perspective view of another alternative embodiment of thecap including curved “dimples.”

FIG. 14H is a side view of the cap of FIG. 14G.

FIG. 14I is a perspective view of the folded cap of FIG. 14G.

FIG. 14J is a side view of the folded cap of FIG. 14I.

FIG. 14K is a perspective view of another alternative embodiment of thecap including flat “dimples.”

FIG. 14L is a side view of the cap of FIG. 14K.

FIG. 14M is a perspective view of the folded cap of FIG. 14K.

FIG. 14N is a side view of the folded cap of FIG. 14M.

FIG. 15A illustrates the positioning of the cap of FIG. 14G or 14K atthe fluid inlets and/or outlets, including the dimples on the cap and ahole in the permeate pack so that the dimples can be glued or weldedtogether through the hole.

FIG. 15B illustrates another view of the cap of FIG. 14G or 14K and 15A.

FIG. 16A is a top view of a series inlet plate.

FIG. 16B is a top view of a series outlet plate.

FIG. 17A is the top view of a permeate pack comprising a stainless steelpermeate screen.

FIG. 17B is a close-up of the permeate passage opening of FIG. 17A,which enables permeate to enter the permeate sheet in the “z” axis.

DETAILED DESCRIPTION

While not to be construed as limiting, the terms used herein have thefollowing definitions unless indicated otherwise.

The term “cross-flow filtration cassette” refers to a type of filtermodule or filter cassette that comprises two end plates and at least oneassembly of sheets positioned therebetween, wherein the at least oneassembly of sheets comprises at least one porous filter element across asurface of which the liquid source material to be filtered is flowed ina tangential flow fashion, for permeation through the filter element ofselected component(s) of the liquid source material. In a cross-flowfilter, the shear force exerted on the filter element by the flow of theliquid source material serves to oppose accumulation of solids on thesurface of the filter element. Cross-flow filters includemacrofiltration, microfiltration, ultrafiltration, and nanofiltration,and low pressure forward osmosis, or reverse osmosis membranes.

As used hereinafter, the term “sheet member” or “sheet” refers to thevarious laminae of the assembly of sheets, the “assembly” or “assemblyof sheets” comprising a stack of generally planar sheet members formingan operative mass transfer unit positioned between assembly end plates.The assembly comprises assembly end plates, permeate sheets, filtersheets, retentate sheets, and optionally permeate screen spacer sheets,coupled to one another in such manner as to permit flow of the fluid tobe separated through the flow channel(s) of the device, for masstransfer involving passage of the permeate through the filter sheets,and retention of the retentate on the side of the filter sheet oppositethe side from which the permeate emerges. The term “compressible” inreference to the retentate sheet or other structural feature or sheetmember of the present invention means that such component or member iscompressively deformable by application of load or pressure thereon.

As defined herein, “caps” or “capped” sheets include the placement of agenerally “U” shaped object at the first end fluid opening (9), at thesecond end fluid opening (12), or both the first end fluid (9) andsecond end fluid (12) openings, so that the structural integrity of thefilter and permeate sheets at said openings does not degrade, bendand/or delaminate as a result of exposure to the turbulent fluid. Thecaps provide additional rigidity to the filter and permeate sheets atsaid openings, thus substantially ensuring that the retentate flowchannel entrances (and exits) remain open and substantially parallel toone another in the assembly, thus allowing for stable retentate flowrates and easier cleaning of the filter cassettes. Advantageously, whenboth ends are capped (i.e, both the first end fluid (9) and second endfluid (12) openings), the assembly's robustness, i.e., ability towithstand permeate backpressure without rupturing, is significantlyimproved, making it more suitable in an industrial environment becauseof the increased robustness.

For the purposes of the instant application, a “module” or a “cassette”or a “filter cassette” “cross-flow module,” or a “filter module” areintended to be synonymous and the terms interchangeable.

For the purposes of the instant application, “retentate flow channel,”“retentate channel,” “flow channel,” and “channel” are intended to besynonymous and the terms interchangeable.

“Liquid source material” or “feed,” as used herein, refers to a liquidcontaining at least one and possibly two or more target substances orproducts of value which are sought to be separated and purified fromother substances present in said liquid. Liquid source materials may forexample be present as aqueous solutions, organic solvent systems, oraqueous/organic solvent mixtures or solutions. The liquid sourcematerial comprising the target substance can be a solid-liquid mixtureor a liquid-liquid mixture.

“Target substance” as used herein refers to the one or more desiredproduct or products to be separated from the liquid source materials.Target substances include, but are not limited to, water, non-biologicalmaterials (e.g., gypsum, minerals, metals, nanostructures,precipitates), inorganic materials, petroleum products and by-products,food and beverage products, biological substances (e.g., cells,proteins, microorganisms, antibodies, hormones, viruses, bacteria,microbes, immunoglobulins, clotting factors, vaccines, antigens,glycoproteins, peptides, enzymes, as well as small molecules such assalts, sugars, lipids, etc.), and renewable fuels and by-products ofmanufacturing renewable fuels (e.g., ethanol, biobutanol, glycerin, andbiodiesel). The target substance can be in the permeate, in theretentate, or both. The target substance can be potable or non-potable.

Because of the dynamic nature of the separation process, a liquid sourcematerial may enter a flow channel, but a retentate will emerge from saidflow channel as permeate is separated therefrom. Retentate can berecirculated and mixed with new liquid source material and furtherseparation effectuated. For the purposes of the present application, tosimplify the explanation of the invention, the term “fluid” will be usedto correspond to a liquid source material, diluted source material, aretentate, a permeate, or any combination thereof, as readily understoodby the person skilled in the art.

For the purposes of the instant application, “cauterization” of thepermeate sheet, for example metal matrix permeate sheet, occurs when thelaser cuts through the metal and the fibers disrupted by the cut areheat bonded or welded to one another.

A generalized embodiment of an assembly of sheets is shown in FIG. 1,comprising a multilaminate array of sheet members of generallyrectangular and generally planar shape with main top and bottom surfacesand a first end and a second end along the longitudinal axis, whereinthe sheet members include in sequence in said array a first assembly endplate (not shown), a first retentate sheet (10), a first filter sheet(20), a permeate sheet (30), a second filter sheet (20), a secondretentate sheet (10), and a second assembly end plate (not shown),wherein each of the assembly end plates, permeate sheet members, andfilter sheet members in said array have at least one fluid cutoutopening (9) at a first end thereof, and at least one fluid cutoutopening (12) at opposite second end thereof, with permeate passageopenings (13) at longitudinal side margin portions of the sheet members.Each of the first and second retentate sheets (10) have at least oneflow channel opening (8) therein, extending longitudinally between thefirst end fluid (9) and second end fluid (12) cutout openings of thepermeate and filter sheets in the array. The sheets are bonded (e.g.,heat, compression, adhesive, heat, or combination thereof) to adjacentsheets about peripheral end and side portions thereof, with their fluidcutout openings and permeate passage openings in register with oneanother, wherein a central portion of each of the sheets is unbonded topermit fluid to flow along the channel opening(s) from the first endfluid (9) to the second end fluid (12) cutout openings such thatpermeate is in contact with, and flows through, the filter sheet (20) tothe permeate sheet (30), and to permit the permeate in the permeatesheet (30) to flow towards the permeate passage openings (13) to thepermeate outlet (not shown in FIG. 1). For ease of disclosure, the firstend fluid (9) and second end fluid openings (12) (and permeate passageopenings (13)) are illustrated in the Figures as generally rectangularor square (see, e.g., FIG. 4A) or as an irregular pentagon (see, FIG.4D). It should be appreciated by the person skilled in the art that theshape of the fluid openings (and permeate passage openings) are notlimited to rectangles or squares or irregular pentagons and can includeany other reasonable shape for the flow of fluid therethrough, asreadily understood by the person skilled in the art.

The assembly of sheets (including assembly end plates) are mountedbetween holder plates, which may be provided with suitable ports, toproduce a filtration cassette, for introduction of liquid sourcematerial to be separated in the filtration cassette, and for dischargeor withdrawal of filtrate/permeate and retentate (see, e.g., FIG. 2).One skilled in the art can appreciate that the assembly end plates canbe integrally sealed to the laminae of sheets. If the integrally sealedassembly comprises assembly end plates made of plastic or polymericmaterials or sheets, the units may provide the function of a disposabledevice for single or multiple use.

As illustrated in FIG. 1, the retentate sheet (10) is provided with aplurality of transversely spaced-apart, longitudinally extending ribs orpartitions (11), such ribs or partitions being of substantially the sameheight and substantially parallel to one another to define a series offlow channel (8) openings between the partitions, wherein the flowchannels (8) extend longitudinally between the position of the first endfluid (9) to the second end fluid (12) cutout openings. The adjacentfilter sheets (20) may optionally be bonded to the ribs or partitions(11) using, for example, a flexible resilient adhesive bonding medium,such as a urethanes, epoxy or silicone adhesive sealant medium, e.g.,applied in a “bead” along the entire circumference of the flow channelopening (8). It should be appreciated that the number of flow channels(8) can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, or more, as readily determined by the person skilled in theart. As a result of the stacking of the sheets in the assembly, eachretentate flow channel (8) preferably has its' own respective entranceand exit (see, e.g., FIG. 2), for example, where liquid source materialenters at one end and retentate exits at the other end of the flowchannel. It should be appreciated by the person skilled in the art thatthe flow in the filtration cassette can be reversed, for example duringcleaning, whereby what was the entrance and exit of the flow channel isnow the exit and entrance, respectively. In dynamic flow, there ispreferably a gel layer that builds on the filter sheet surface exposedin the retentate flow channel. The optimal gel layer conditions (depthand density) are found by manipulating pressure and shear along theretentate flow channel (8) and hence across the surface of the filtersheet (20).

The permeate sheet (30) may constitute a foraminous material of fromabout 80 to about 300 mesh size. Examples of permeate sheets include,but are not limited to, woven materials, nonwoven materials, moldedporous materials, or combinations thereof. For example, the foraminouspermeate sheets may comprise a woven polymeric mesh including, but notlimited to, polyester, polypropylene, nylon, fluorocarbon polymers suchas polytetrafluoroethylene, polyethylene, polysulfone, polyethersulfone,polyetherimide, polyimide, polyvinylchloride, ceramics, e.g., oxides ofsilicon, zirconium, and/or aluminum, and composites comprising one ormore of such materials. Alternatively, the permeate sheets may comprisea nonwoven material, of suitable foraminous character. In oneembodiment, the permeate sheet is a reinforced polymer composite.

The filter sheets (20) may be of any suitable porous, malleablematerials including, but not limited to, woven or non woven materials,stretched materials, irradiated materials, wet phase inversionmaterials, dry phase inversion materials, cast materials, orcombinations thereof. Examples of materials include, but are not limitedto, cellulose, polyphenylene oxide, polysulfone, cellulose nitrate,cellulose acetate, regenerated cellulose, polyether amide, polyphenyleneoxide/polysulfone blends, mixed esters of cellulose, polyamide,polyvinylidene difluoride, thin film composite (TFC), polyacrylonitrile, mixed ester cellulose, polypropylene, polytetra fluoroethylene, polyester, polycarbonate, high density polyethylene, andpolyethersulfone. The filter sheets can include woven or non-wovenmaterials.

Presently, the filtration cassettes of the prior art are only rated fortemperatures less than about 60° C., while many industrial processes arecarried out at temperatures greater than 60° C. The United States FoodSafety and Inspection Service (FSIS) define the danger zone wherebacteria can grow as roughly 5 to 60° C. Processing above 60° C. istherefore beneficial. Towards that end, preferably, the assembly endplates, filter sheets, the retentate sheets, and permeate sheets (andthe optional permeate screen spacer sheets) are made of materials whichare adapted to accommodate high temperatures and chemical sterilants, sothat the interior surfaces of the filtration cassette are able towithstand higher processing temperature and/or extreme pH and may besteam sterilized and/or chemically sanitized solutions for regenerationand reuse, as “steam-in-place” and/or “sterilizable in situ” structures,respectively. Steam sterilization typically may be carried out attemperatures on the order of from about 121° C. to about 130° C., atsteam pressures of 15-30 psi, and at a sterilization exposure timetypically on the order of from about 15 minutes to about 2 hours, oreven longer. Further, the ability to operate the filter cassettedescribed herein using higher temperature fluid is advantageous. It iswell known in the art that there can be benefits to working with ahigher temperature fluid, as will be discussed below. Alternatively, theentire cassette may be formed of materials which render the cassettedisposable in character.

Although not shown, an assembly of sheets comprises two assembly endplates, one on each side of the stacked array shown in FIG. 1. Theassembly end plates may be formed of any suitable materials ofconstruction, including, for example, stainless steel or other suitablemetal, or polymers such as polypropylene, polysulfone, polyetheretherketone and polyetherimide. A filtration cassette comprises at least oneassembly of sheets as well as a holder inlet plate and a holder outletplate, wherein the holder plates function as the fluid manifold andcompress the assembly of sheets therebetween. Preferably the assemblyend plates comprise polymeric material while the holder plates comprisestainless steel or other suitable materials such as metals, polymers, orany combination thereof.

As introduced hereinabove, disadvantageously, the sheet material at theleading edge of the first end fluid (9) and/or the second end fluid (12)cutout openings of the prior art can degrade in several ways duringheavy use over time, wherein the turbulence associated with the fluid atthe retentate flow channel (8) entrances results in deformation of thesheet material and subsequence blocking at said entrances, as shown inFIG. 3B (e.g., compare FIG. 3A to FIG. 3B). Further, for example, incellulosic or fluid streams with fibrous components, fibers and otherirregular solids in the fluid can bridge the flow channel entrances.Once a few fibers and other irregular solids are caught in the prior artdesign there is cascade effect whereby they rapidly accumulate until theentrance to the retentate flow channel is no longer open.

As introduced herein, the assembly of sheets comprises a “base sequence”of sheets positioned between two assembly end plates (hereafterdesignated by the symbol “E”), wherein the base sequence of sheets inthe assembly comprise, consist of, or consist essentially of, a firstretentate sheet (hereafter designated by the symbol “R”), a first filtersheet (hereafter designated by the symbol “F”), a foraminous permeatesheet (hereafter designated by the symbol “P”), and a second filtersheet (“F”). The assembly can have the general formulaE/R/(F/P/F/R)_(n)/E, wherein n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or moredepending on the circumstances. In a first aspect of the invention, thecombination of sheets F/P/F, or the “permeate pack,” are “capped” at thefirst end fluid (9) cutout opening, the second end fluid (12) cutoutopening, or both. An illustrative array of sheets in the assembly mayfor example feature the sheet sequence E/R({circumflex over( )}F/P/F{circumflex over ( )}R)_(n)/E, wherein the capped F/P/F sheetsare separated from the retentate sheets by the {circumflex over ( )}symbol.

Referring to FIGS. 4A-4C and FIGS. 5A-5C, the caps or reinforcement atthe first end fluid openings (9) can be seen. As shown in the figures,the first end fluid openings (9) have four sides. Fluid that enters theinlet is directed down the first end fluid opening (9) and some of thefluid makes an approximately 90° turn down the very first flow channelentrance provided at first retentate sheet “R.” The remainder of thefluid continues along the first end fluid opening (9) past a cappedF/P/F combination and some of the fluid makes an approximately 90° turndown the next retentate flow channel entrance provided by the nextretentate sheet “R,” and so on. Notably, the cap is on at least aportion of the first end fluid opening (9) proximate to the retentateflow channel entrance so that some of the fluid can make theapproximately 90° turn into the retentate flow channel entrance, whileminimizing damage to the F/P/F combination (e.g., as shown in FIG. 3B).The other three sides of the F/P/F combination of sheets is fused,bonded, or attached to the retentate sheet “R.”

FIG. 5A is a perspective view of FIG. 4A showing a first filter sheet(20), a permeate sheet (30), and a second filter sheet (20) havingcapped (22) first end fluid openings (9). FIG. 5B is a cross-sectionalview of FIG. 4A along A-A′ showing the first filter sheet (20), apermeate sheet (30), and a second filter sheet (20) having capped (22)first end fluid openings (9). The cap (22) has the general cross-sectionof a “U” (see for example, FIG. 4C), and transverses the F/P/F sheets,i.e., the permeate pack, through the first end fluid openings (9) of theF/P/F combination such that one leg of the “U” at least partiallyoverlaps a first side (25) (see, FIG. 5B) of the first filter sheet (20)and the other leg of the “U” at least partially overlaps a second side(26) (see, FIG. 5B) of the second filter sheet (20), with the permeatesheet (30) positioned therebetween. A photo of the cap on the F/P/Fsheets can be seen in FIG. 5C. FIG. 4A illustrates a top plan view ofeither the first side of the first filter sheet or the second side ofthe second filter sheet, wherein only one leg of the “U” cap can beseen. Referring to FIG. 4B, it should be appreciated that the at leastpartial overlap of the cap (22) (i.e., the legs of the “U”) is notlimited to a rectangular shape but can be rounded, be triangular, betrapezoidal, as well as other shapes easily envisioned by those skilledin the art. FIG. 5D is a perspective view of the components of anassembly of the first aspect, including the installed caps (22) over theF/P/F sheets, wherein the assembly end plates are not shown. It shouldbe appreciated that instead of the U-shaped cap, the first end fluidopening (9) of the F/P/F sheets can be stiffened using rigid adhesives,solid sheets of rigid materials such as plastic or metals, coatings,tape, radio frequency sealing or melting the polymeric components of thepermeate pack in the immediate area of the flow channel entrances,however, stainless steel “U” caps provided a superior outcome for therectangular fluid openings (9, 12).

The figures show and the description describes the assembly as havingcaps or reinforcement only over a portion of the first end fluidopenings (9) that are in register with one another for the parallel flowof fluid (see, e.g., FIG. 13A). It should be appreciated that withparallel flow, the fluid flows in one direction within an assembly andbetween assemblies in the filter cassette. That said, the series flow offluid is contemplated, wherein you can have series flow within anassembly, between assemblies, or both (see, e.g., FIG. 13B wherein thefluid flows in a first direction (i.e., from the first end to the secondend) along the flow channels (8) in one assembly and make a 180 degreeturn to flows in a second direction (i.e., from the second end to thefirst end) along flow channels (8) of the next assembly in a serpentinefashion). In the case of series flow, the caps are placed on some of thefirst end fluid openings as well as some of the second end fluidopenings, depending on the nature of the series flow (i.e., whetherseries within the assembly or between assemblies or both), as readilyunderstood by the person skilled in the art. It is further understoodthat caps may be present on both the first end and the second end fluidopenings to improve the assembly's robustness and/or retainfunctionality in the case of need to reverse the fluid flow direction.With the series flow filter cassette, additional layers in the array arenecessary to ensure that the fluid follows a serpentine path through thefilter cassette. For example, the series inlet plate (50) in FIG. 16Aand the series outlet plate (60) in FIG. 16B can be used to redirect theflow of fluid. An example of a series flow filter cassette, wherein theseries flow is between assemblies, isHIP/RG/A₁/RG/SI/RG/A₂/RG/SO/RG/A₁/RG/HOP, where HIP is the holder inletplate (having a first end inlet), RG is a rubber gasket, A₁ and A₂ areassemblies as described herein, SI is a series inlet plate (e.g., (50)in FIG. 16A), SO is a series outlet plate (e.g., (60) in FIG. 16B), andHOP is the holder outlet plate (having a second end inlet). Theassemblies A₁ and A₂ can have the sheet sequence E/R/(F/P/F/R)_(n)/E,wherein n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18,19, 20, or more. As described above, the caps are placed at a second endin A₁ (see, FIG. 16A), and then in A₂, the caps are placed at the firstend (see, FIG. 16B), and so on. Because of the series inlet and theseries outlet plates, the fluid flows in a serpentine fashion from thefirst assembly to the second assembly to the third assembly and so on.It is noted that there may still be parallel flow within each assembly,or the assembly may be constructed to have series flow within theassembly, as readily understood by the person skilled in the art.Further, it should be appreciated that the value of “n” may be the sameas or different from one another from assembly to assembly, as readilyunderstood by the person skilled in the art. It is thought that the capsare even more important in the series apparatus because of the 180° turnthat the fluid will have to make, resulting in even greater turbulencewithin the filter cassette.

The caps can be made of any material that does not interact or isreactive with fluids being introduced into the filtration cassette. Suchmaterial may include, but is not limited to, metals, ceramics, polymericmaterials, and combinations thereof. Preferred metals include silver,copper, nickel, and stainless steel. Preferred polymeric materialincludes thermoset plastics such as amino, epoxy, phenolic, andunsaturated polyesters. The polymeric materials can be molded to have asmooth or textured inside, with or without inside features designed tomore substantially bond with the F/P/F permeate pack, and are preferablyresistant to higher temperatures and varied pH values. An advantage ofusing polymeric caps include, but is not limited to, thermalcoefficients that are similar to those of the permeate sheet whichcorresponds to similar expansion and contraction rates. With regards tothe stainless steel caps, the inside can be smooth or textured (e.g.,chemical etch or sandblasted), with or without inside features designedto more substantially bond with the F/P/F permeate pack. The insidefeatures designed to assist with the bonding to the permeate packinclude, but are not limited to, at least one clip (see, for example,FIGS. 14A-14B and FIGS. 14C-14D), at least one “hook” (see, FIG.14E-14F), or at least one dimple (see, FIGS. 14G-14N). It should beappreciated by the person skilled in the art that the caps can be somecombination of the options described herein. The caps can be scored orthe radius deliberately weakened on the inside so that the cap collapsesfully when compressed, as understood by the person skilled in the art.Further, it should be appreciated that the shape of the dimples andhooks are not limited to circles and squares, respectively, but can beany shape that ensures that the caps bond with the permeate packmaterials.

The assembly of sheets described herein is manufactured as follows. Thepermeate packs, i.e., the F/P/F combination, are die cut and bonded.Thereafter, the cap is secured to the permeate pack, either by glue orother bonding material or by welding together. For example, a controlledamount of bonding material (e.g., epoxy, polyurethane) can be dispensedinto the cap, for example using a syringe, and then the cap ispositioned and clamped on the permeate pack as described herein. The“controlled amount” corresponds to an amount of bonding material suchthat when the cap is clamped there is a substantially full spreadbeneath the cap to cover the cap's surface but not so much as to haveexcess bonding material squeezing out from beneath the cap. In oneembodiment, the cap has at least one dimple (see, FIGS. 14G-14N),wherein a hole is provided in the permeate pack so that the dimples canbe glued or welded together through the hole. In another embodiment, thecap has at least one hook (see, FIGS. 14E-14F), wherein a hole matchingthe shape of the hook is provided in the permeate pack such that theindents of the hook would be caught in said hole so that the cap cannotbe pulled out. In still another embodiment, the cap's open ends canextend through an opening cut into the permeate pack and be bonded,welded, or otherwise sealed together to bond the open ends of theU-shaped cap together and form an integral seal (see, e.g., FIGS. 15Aand 15B). Thereafter, the permeate pack can be attached to the retentatesheets as understood by the person skilled in the art. It is to beunderstood that this is only one embodiment of positioning the caps onthe permeate packs and is not intended to limit the invention in anyway. Alternative methods are readily envisioned by the person skilled inthe art.

Advantageously, the cap or reinforcement of the first aspect over theF/P/F sheets ensures that the entrances at the retentate flow channelsdo not fold or collapse over time due to the turbulence associated withthe fluid entering the cassette. This ensures that the entrances to theretentate channels are not blocked and that the adjacent filter sheetsare substantially parallel to one another, thus increasing the workingsurface area of retentate channels, resulting in a higher flux rate thanwithout the caps. Moreover, the caps minimize the accumulation of fibersand other irregular solids at the entrances. Because the clips are sorigid and are substantially parallel to one another, particulatematerial that is larger than the entrance to the flow channels cannotenter the flow channels and foul up the filter sheets. Further, thefilter cassettes are easier to clean, as can be seen in FIG. 6A (beforecleaning) and 6B (after cleaning), such that the lifespan of the filtercassette with the caps is longer than the lifespan of a filter cassettewithout the caps, under the same operating conditions. The cleaning ofthe filter cassettes described herein can be more aggressive because ofthe inclusion of the caps. Another advantage is that the filtercassettes with caps are more resistant to higher temperatures than anyof the filter cassettes of the prior art. Initial temperature ratings ofthe filter cassettes with caps, as described herein, are 85° C., buttemperatures in excess 121° C. have been tested with success.Accordingly, the ability to utilize the modules that comprise the capsor reinforcement of the first aspect at higher temperatures reducesprocessing costs. Accordingly, in one embodiment, liquid sourcematerials having temperatures in a range from about 1° C. to about 130°C. can be introduced into the filter cassettes of the first aspect.Other temperature ranges contemplated include about 50° C. to about 130°C., about 50° C. to about 85° C., greater than 60° C. to about 130° C.,and greater than 60° C. to about 85° C. It is especially preferred thatthe temperature range be above 60° C. when the source material isedible. It should be appreciated that if the liquid in the liquid sourcematerial has a freezing point below zero that the filter cassettesdescribed herein can be used for separation of the target substance attemperatures below zero, so long as the temperatures are above thefreezing point of the liquid.

It should also be appreciated by the person skilled in the art thatfilter cassettes without caps may be retrofitted with caps, for example,using the procedures described herein.

In a second aspect, the fluid opening (9), and optionally the fluidopening (12) (not shown), is cut in a shape other than a rectangle. Asshown in FIGS. 4D and 4E, the fluid opening (9) is cut in the shape ofan irregular pentagon, having a “V” substituted at one side of arectangle, to be positioned proximate to the channel entrances of theretentate sheets. The advantage associated with the irregular pentagonfluid opening is the increased stiffness at the leading edge relative tothat of a traditional rectangular fluid opening, which tends to foldover as a result of the turbulent fluid (see, e.g., FIG. 3B). Withoutbeing bound by theory, it is thought that the irregular pentagon openingof FIGS. 4D and 4E will add stiffness and minimize the force of thefluid flow through the channel and as such, will not fold over in thesame manner as the rectangular opening. It should be appreciated thatthe irregular pentagon-shaped fluid opening may be capped, similar tothat described in the first aspect. Further, the filtration cassette maybe designed to be in parallel, wherein the irregular pentagon-shapedfluid opening is always at the first end (9), or the filtration cassettemay be in series wherein the irregular pentagon-shaped fluid opening isat the first end (9) and the second end (12), depending on the seriesarrangement, as described hereinabove in the first aspect.

In a third aspect, the assembly comprises at least one permeate screenspacer (hereafter designated by the symbol “S”). An illustrativeassembly may for example feature the sheet sequenceE/R/(F/S/P/S/F/R)_(n)E, wherein n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, or more. Another illustrative assemblymay for example feature the sheet sequence E/R/(F/S/P/F/R)_(n)E, whereinn=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,or more. Still another illustrative assembly may for example feature thesheet sequence E/R/(F/P/S/F/R)_(n)E, wherein n=1, 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more. Yet anotherillustrative assembly may for example feature the sheet sequenceE/R/(F/P/S/P/F/R)_(n)E, wherein n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, or more.

FIG. 7A illustrates the prior art F/P/F permeate pack structure, whereinthe filter sheet is on either side of a permeate sheet. Duringfiltration the fluid is under pressure (e.g., from about 2 to about 300psi) to incentivize permeate to pass through the filter sheet (20) andexit via the permeate sheet (30) through the permeate flow channels(see, e.g., (13) in FIG. 1). Disadvantageously, some inherent throughputrestriction results from the interfacial tortuosity of the permeatesheet material being in direct contact with most filter sheets. Thisoccurs wherever materials on one layer cover what would otherwise beopen area on the adjacent layer(s). Pressurization of fluid from eitherside of the permeate sheet causes some flex of the filter sheet furtherinto the open area thus worsening the throughput restriction. Forexample, by including the first and second permeate screen spacerbetween the filter sheet and the permeate sheet, to yield thecombination F/S/P/S/F (see, FIG. 8), permeate restriction between thetwo filter sheets can be minimized and lateral flow can be enabled. Thisis true for the other illustrative assemblies disclosed herein. Withoutbeing bound by theory, it is thought that the inclusion of the permeatescreen spacer decreases the aggregate area of blinding from contactpoints, hence minimizing the permeate restriction and enabling thelateral flow (see, e.g., FIG. 9B). Further, the inclusion of thepermeate screen spacer increases the stiffness, minimizing retentateflow channel bulging, thus retaining uniform flow characteristics athigher pressure and shear.

In one embodiment, the permeate screen spacer (40) has large open areas,e.g., on the order of about 20% to about 80%, preferably about 35% toabout 70%, even more preferably about 50% to about 65%, relative to thesmaller open area of the filter sheet (20), which has minimal open area(e.g., in a range from about 1% to about 5%) and the permeate sheet(30), wherein the permeate sheet has open area in a range from about 30%to about 60%, preferably about 40% to about 50% (see, e.g., FIG. 9A).Alternatively, the permeate screen spacer can have open areas of about20% to about 35% or about 70% to about 80%. The pattern on the permeatescreen spacer (40) is not limited to that shown in FIG. 9A but caninclude patterns such as those shown in FIGS. 10A-D, as well as otherpatterns easily envisioned by the person skilled in the art. The screenof the permeate screen spacer, i.e., the “non-open” areas, may be rigid,semi-rigid, or flexible, depending on the use, as readily determined bythe person skilled in the art. The screen of the permeate screen spacercan comprise any suitable material of construction including, but notlimited to, natural or synthetic polymers, silicone, ceramics, metals,polymeric fluorocarbons, compatible alloys, or any combination thereof.For example, polymers such as polypropylene, polyethylene, polysulfone,polyethersulfone, polyetherimide, polyimide, polyvinylchloride,polyester, etc.; nylon, silicone, urethane, regenerated cellulose,polycarbonate, cellulose acetate, cellulose triacetate, cellulosenitrate, mixed esters of cellulose, etc.; ceramics, e.g., oxides ofsilicon, zirconium, and/or aluminum; metals such as stainless steel;polymeric fluorocarbons such as polytetrafluoroethylene; and compatiblealloys, mixtures and composites of such materials. The permeate screenspacer may be woven or non-woven. It should be appreciated that thepermeate screen spacers in the assembly may be the same as or differentthan the other permeate screen spacers. Further, the permeate screenspacers in one assembly may be the same as or different than thepermeate screen spacers in another assembly.

Optionally, the assembly comprising at least one permeate screen spacercan have: (i) “caps” at the fluid openings per the first aspect, asillustrated in FIG. 11; (ii) irregular pentagon-shaped fluid cut-outopenings per the second aspect; or (iii) both (i) and (ii). When capped,an illustrative assembly of the third aspect may for example feature thesheet sequence E/R({circumflex over ( )}F/S/P/S/F{circumflex over( )}R)_(n)/E, wherein the capped F/S/P/S/F sheets are separated from theretentate sheets by the {circumflex over ( )} symbol. Anotherillustrative assembly of the third aspect may for example feature thesheet sequence E/R({circumflex over ( )}F/S/P/F{circumflex over( )}R)_(n)/E, wherein the capped F/S/P/F sheets are separated from theretentate sheets by the {circumflex over ( )} symbol. Still anotherillustrative assembly of the third aspect may for example feature thesheet sequence E/R({circumflex over ( )}F/P/S/F{circumflex over( )}R)_(n)/E, wherein the capped F/P/S/F sheets are separated from theretentate sheets by the {circumflex over ( )} symbol. Yet anotherillustrative assembly of the third aspect may for example feature thesheet sequence E/R({circumflex over ( )}F/P/S/P/F{circumflex over( )}R)_(n)/E, wherein the capped F/P/S/P/F sheets are separated from theretentate sheets by the {circumflex over ( )} symbol. The caps areidentical in material and manufacture as the caps discussed hereinabovein the first aspect.

In a fourth aspect, at least one permeate sheet (30) in the filtrationcassette described herein can comprise a metal matrix, or otherstiffened or reinforced porous material. For the purposes of thisaspect, reference to a metal matrix hereinafter does not foreclose theuse of another stiffened or reinforced porous material instead.Preferably, the permeate sheets (or the permeate sheets with at leastone permeate screen spacer) have enough structural integrity orstiffness to ensure channels between the filter sheets (20) on eitherside of the permeate sheet (30) exist, thus ensuring that the filtersheets remain separate and substantially parallel to one another, whichwill improve the flux rate. For example, the permeate sheet (30) maycomprise metal material, e.g., a stainless steel material such as anindexed stainless steel material that has been diffusion bonded at thewire intersections (see, e.g., FIG. 12). Indexing is a technique wherethe weave is rotated to increase strength with minimal loss inpermeability. The successful use of the stainless steel permeate sheetdescribed herein is surprising as the filtration cassettes of the priorart comprising stainless steel permeate sheets (e.g., having stainlesssteel fibers that would shed) always succumbed to punctures, which ledto contamination of permeates or a fatal breach of filter integrity.When the permeate sheet used in the assembly is stainless steel or areinforced porous material, the permeate sheet may also function as aretentate flow channel stiffener by improving the resistance toretentate channel flex as well as ensuring an adequate channel exit forthe permeate flow. Moreover, when the permeate sheet has the requisitestiffness, the caps of the first aspect are optional. In one embodiment,the permeate sheet (30) comprises an indexed stainless steel materialthat is fully diffusion bonded stainless steel with all ports and edgeslaser cut then deburred, eliminating any stray fibers to dislodge thatmay damage the filter sheets (20). The added stiffness enables theretentate flow channel to retain its shape, and allows the fluid to runat a higher sheer and at higher flux rate for a longer period of timebefore cleaning is required. Without being bound by theory, it isexpected that minimizing the number of cleanings will significantlyincrease the life of the product. It should be appreciated that all, orless than all, of the permeate sheets in an assembly of sheets maycomprise a metal matrix, or other reinforced porous material. Forexample, every permeate sheet, or every second, third, fourth, etc.,permeate sheet in the assembly can be a metal matrix, or otherreinforced porous material. Further, it should be appreciated when thefiltration cassette comprises at least two assemblies positioned betweenthe holder plates, the assemblies may be the same as or different fromone another in terms of the type and number of metal matrix (or otherreinforced porous material) permeate sheets present.

An embodiment of the metal matrix permeate sheet is shown in FIGS.17A-B. FIG. 17A is the top view of a permeate pack comprising two filtersheets with a stainless steel permeate sheet sandwiched therebetween.For the purposes of describing FIGS. 17A-B, an x,y,z axis is provided,wherein the sheets are in the x-y plane. FIG. 17B is a close-up of thepermeate passage opening of FIG. 17A, which enables permeate to enterthe permeate passage opening (13) along the z axis. Because the permeatepassage openings in the metal matrix permeate sheet have to be cut,e.g., laser cut, and cauterized, the permeate passage opening (13) onthe metal matrix permeate sheet can have a narrower width than thepermeate passage opening of the filter sheet(s), the retentate sheet(s),and the assembly end plates (and optional spacer permeate screensheet(s)). For example, the width of the permeate passage opening of thefilter sheet (and retentate sheet and assembly end plates and optionalspacer permeate screen sheet) is shown as “i” while the width of themetal matrix permeate sheet is shown as “j.” The value of “j” ispreferably between 65% and 80% of the value of “i.” Without the inset,the permeation rate may be restricted due to sealing off or blinding ofthe edges of the permeate passage openings in the metal matrix permeatesheet following laser cutting of the permeate passage openings. With theinset, permeate can enter the permeate passage opening with lessrestriction along the z axis. It should be appreciated that the inset isone embodiment of the assembly comprising metal matrix permeatesheet(s). Alternatives include an assembly wherein the width of thepermeate passage opening in the metal matrix permeate sheet can be equalto the width of the permeate passage opening of the other sheets in theassembly.

Accordingly, for any of the assemblies of any of the aspects describedherein, the width of the permeate passage opening in the permeatesheet(s) can be less than or equal to the width of the permeate passageopening of the other sheets in the assembly, regardless of the materialof the permeate sheet, wherein the other sheets in the assembly areselected from the group consisting of filter sheets, retentate sheets,permeate sheet spacers, and any combination thereof.

Another advantage associated with the use of metal matrix permeate sheetincludes the ability to operate the filter cassette using highertemperature fluid. It is well known in the art that there can bebenefits to working with a higher temperature fluid because theviscosity of the fluid can decrease as the temperature increases. As aresult, the permeate flux passage is improved with a concomitantdecrease in the energy expenditure and processing costs. Further,smaller capacity pumps can be used and heat exchangers and buffer tankscan be eliminated. Another advantage is the ability to achieve a higherpercentage solids target at a higher temperature relative to thatachieved at the lower temperatures of the prior art.

Still another advantage associated with the use of metal matrix permeatesheet includes a filter cassette that is suitable for sonication.Sonication is a low energy means that can be used to enhance throughputin the filtration cassette by substantially preventing occlusion orblinding of the filter sheet surface porosity as well as minimizingfouling/clogging of the retentate flow channels. The addition of a metalpermeate sheet that is installed immediately under, but also in contactwith filter sheets, enables uniform transmission of the sonic waves dueto uniform proximity of the stainless steel permeate sheet to the filtersheets. Uniform transmission is important to functionality because toolow an intensity will not sufficiently agitate, resulting in a gel layerthat is too thick (i.e., not an optimal gel layer), while too high anintensity will cause a loss of sheet integrity because of physicaldamage, such as from acoustic cavitation. Prior art attempts atultrasonic agitation of polymeric membrane sheets have been ineffectivebecause the intensity needed to clean the zones furthest from theacoustic field were too great for the zones closest to the acousticfield. The advantage of the geometry described herein is that a lowerintensity and a lower sonication rate can be used because each metalmembrane surface in each permeate pack is being agitated duringultrasonic generation. Other advantages associated with sonicationinclude, but are not limited to, the improvement of reaction time ofchemical and biological processes because of mixing function, anincrease of the gas transfer coefficient, and aerating and mixing (e.g.,bubble dispersement criticality).

Accordingly, the fourth aspect described herein further relates to amethod of sonicating the filtration cassette described herein, saidmethod comprising introducing an acoustic field or wave to a filtrationcassette, and generating ultrasound waves to enhance throughput in thefiltration cassette and/or fouling/clogging of the retentate flowchannels, wherein the filtration cassette comprises at least oneassembly, wherein the at least one assembly comprises:

-   -   a multilaminate array of sheet members of generally rectangular        and generally planar shape, each sheet having a first end and a        second end longitudinally opposite the first end and a        thickness, wherein the sheet members comprise in sequence in        said array a first retentate sheet, (a first filter sheet, a        metal matrix permeate sheet, a second filter sheet, and a second        retentate sheet)_(n), wherein each of the first filter sheet,        the metal matrix permeate sheet, and the second filter sheet        members in said array have at least one fluid opening at the        first end thereof, and at least one fluid opening at the second        end thereof, wherein the first end fluid opening(s) of the array        are in register with one another and the second end fluid        opening(s) of the array are in register with one another, and        wherein n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more, wherein the        first and second retentate sheets have at least one channel        opening therein, each channel opening extending longitudinally        between the first end fluid opening(s) and the second end fluid        opening(s) in the array and wherein the at least one channel        opening is open through the entire thickness of the first and        second retentate sheets to permit a fluid to contact the        adjacent filter sheets, and wherein the first and second        retentate sheets are bonded to the adjacent filter sheets about        peripheral end and side portions thereof; and    -   two assembly end plates sandwiching the multilaminate array of        sheets, wherein the two assembly end plates comprise at least        one fluid opening at the first end thereof, and at least one        fluid opening at the second end thereof, or both, in register        with the fluid openings of the array,    -   wherein the at least one assembly further comprises at least one        permeate passage opening at longitudinal side margin portions of        the assembly(s).

The filter cassette for the sonication method can further comprise atleast one of options (I), (II), or (III), or any combination of(I)-(III): (I) a cap positioned on at least a portion of the first endfluid opening(s) or at least a portion of the second end fluidopening(s), or both, of a permeate pack, wherein the permeate packcomprises the first filter sheet, the metal matrix permeate sheet, andthe second filter sheet members, wherein the cap is positioned proximateto the channel openings of the first and second retentate sheets; (II)the fluid openings at the first end, the fluid openings at the secondend, or both the fluid openings at the first and second end, are cut asan irregular pentagon having a “V” positioned proximate to the channelopenings of the first and second retentate sheets; or (III) a firstpermeate screen spacer positioned between the first filter sheet and themetal matrix permeate sheet or a second permeate screen spacerpositioned between the second filter sheet and the metal matrix permeatesheet, or both, wherein the permeate screen spacer(s) comprise fluidopenings in register with the fluid openings of the array. Further, withregards to the filter cassette for sonication, a width of the permeatepassage opening of the permeate sheet can be less than, or equal to, awidth of the permeate passage opening of each of the filter sheets andretentate sheets in the multilaminate array of sheets.

A fifth aspect of the invention relates to a filtration cassettecomprising at least one, two, three or four of: (a) caps or otherreinforcement at the fluid openings (i.e., the first aspect); (b) theirregular pentagon-shaped fluid openings (i.e., the second aspect); (c)the permeate screen spacers (i.e., the third aspect); and (d) thestiffened permeate sheets (i.e., the fourth aspect), in any combination,as readily understood by the person skilled in the art. In other words,the filtration cassette may comprise, consist of, or consist essentiallyof: just one of (a), (b), (c), or (d); the combination of [(a) and (b)],[(a) and (c)], [(a) and (d)], [(b) and (c)], [(b) and (d)], or [(c) and(d)]; the combination of [(a), (b) and (c)], [(a), (b) and (d)], [(b),(c) and (d)], [(a), (c) and (d)]; or the combination of [(a), (b), (c),and (d)], depending on the chemical and physical characteristics of thepermeate and the retentate, as readily understood by the person skilledin the art.

In a sixth aspect, a permeate pack is described, said permeate packcomprising at least three sheet members of generally rectangular andgenerally planar shape, each sheet having a first end and a second endlongitudinally opposite the first end, wherein the sheet memberscomprise a first filter sheet, a permeate sheet, and a second filtersheet, wherein each sheet has at least one fluid opening at the firstend thereof, and at least one fluid opening at the second end thereof,wherein the first end fluid opening(s) of the array are in register withone another and the second end fluid opening(s) of the array are inregister with one another, wherein each sheet further comprises at leastone permeate passage opening at longitudinal side margin portions ofeach sheet, wherein each permeate pack comprises a cap positioned on atleast a portion of the first end fluid opening(s) or at least a portionof the second end fluid opening(s), or both, and a width of the permeatepassage opening of the permeate sheet can be less than, or equal to, awidth of the permeate passage opening of each of the filter sheets inthe permeate pack. The permeate pack may optionally comprise a firstpermeate screen spacer positioned between the first filter sheet and themetal matrix permeate sheet or a second permeate screen spacerpositioned between the second filter sheet and the metal matrix permeatesheet, or both. The permeate sheet can comprise, consist of, or consistessentially of material selected from the group consisting of natural orsynthetic polymers (e.g., polypropylene, polyethylene, polysulfone,polyethersulfone, polyetherimide, polyimide, polyvinylchloride,polyester, nylon, silicone, urethane, regenerated cellulose,polycarbonate, cellulose acetate, cellulose triacetate, cellulosenitrate, mixed esters of cellulose), silicone, ceramics (e.g., oxides ofsilicon, zirconium, and/or aluminum), polymeric fluorocarbons (e.g.,polytetrafluoroethylene), metals (e.g., stainless steel), compatiblealloys, or any combination thereof. The cap(s) are understood to includethose described herein in the first aspect. In one embodiment, thepermeate sheet comprises, consists of, or consists essentially ofstainless steel. In another embodiment, the permeate sheet comprises,consists of, or consists essentially of stainless steel and a width ofthe permeate passage opening of the permeate sheet can be less than awidth of the permeate passage opening of each of the filter sheets inthe permeate pack.

The methodology of the present invention permits a target substance tobe separated from a liquid source material by the simplest mechanicalmeans. The liquid source material can be a solid-liquid mixture or aliquid-liquid mixture, wherein the liquids can be at least one ofaqueous, semi-aqueous, or organic. The target substance can be thepermeate, the retentate, or both, including, but not limited to, water,non-biological materials (e.g., gypsum, minerals, metals,nanostructures, precipitates), inorganic materials, petroleum productsand by-products, food and beverage products, and biological substances(e.g., cells, proteins, microorganisms, etc.). The target substance canbe potable or non-potable.

In the use of cross-flow filtration cassettes, the specificity and speedof a desired separation is effected by a number of factors including,but not limited to, a) fluid distribution in the cross-flow module, b)channel height of the cross-flow module, c) channel length, d) shearrate, e) sheet pore structure, f) sheet structure, g) sheet chemistry,h) trans-membrane pressure, i) osmotic force, j) hydrophobic/hydrophilicdifferential, k) liquid source material modification, l) temperature,and m) pressure drop, which is a function of applied pressure channellength, velocity and solution viscosity.

Importantly, the cross-flow filtration cassettes can be in series or inparallel with reactor vessels and/or additional cross-flow filtrationcassettes, as readily understood by the person skilled in the art.Depending on the arrangement of the apparatus, optimal rates ofproduction and separation of a target product can be accomplished.

A seventh aspect relates to a method of separating one or more targetsubstances from a liquid source material, said method comprising:

flowing the liquid source material into at least one filtration cassetteof the fifth aspect, as described herein, so as to recover a permeatefluid for disposal, reuse, further filtration, or as a target product;and

recovering a retentate stream for disposal, reuse, further filtration,or as a target product.

In the method of the seventh aspect, optionally the liquid sourcematerial is diluted with a diluent in an amount sufficient to reduce theviscosity of the liquid source material if the liquid source material isviscous, to form a continuous stream of diluted source material forintroduction to the at least one filtration cassette or filtrationmodule. Further, if needed, a diafiltration medium, e.g., buffer, can beintroduced to the liquid source material or diluted source material toassist in the recovery of the target substance in the permeate fluid, asreadily understood by the person skilled in the art. Additionally, thetemperature of the liquid source material can be raised to a range ofabout 5° C. to about 130° C. to reduce the viscosity of the liquidsource material if the liquid source material is viscous, to form acontinuous stream of heated source material for introduction to the atleast one filtration cassette or filtration module.

Although the invention has been variously disclosed herein withreference to illustrative embodiments and features, it will beappreciated that the embodiments and features described hereinabove arenot intended to limit the invention, and that other variations,modifications and other embodiments will suggest themselves to those ofordinary skill in the art, based on the disclosure herein. The inventiontherefore is to be broadly construed, as encompassing all suchvariations, modifications and alternative embodiments within the spiritand scope of the claims hereafter set forth.

That which is claimed is:
 1. A filtration cassette comprising at leastone assembly, wherein the at least one assembly comprises: amultilaminate array of sheet members of generally rectangular andgenerally planar shape, each sheet of the array having a first end, asecond end longitudinally opposite the first end, and a thickness,wherein the sheet members comprise in sequence in said array, a firstretentate sheet, (a permeate pack and a second retentate sheet)_(n),wherein n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more, wherein the permeatepack comprises a first filter sheet, a permeate sheet, and a secondfilter sheet, wherein each sheet in each permeate pack has at least onefluid opening at the first end thereof and at least one fluid opening atthe second end thereof, wherein corresponding fluid openings at thefirst end of each sheet in each permeate pack are in register with oneanother and corresponding fluid openings at the second end of each sheetin each permeate pack are in register with one another, wherein thefirst and second retentate sheets have at least one channel openingtherein, each channel opening extending longitudinally between a firstchannel entrance positioned proximate to fluid openings at the first endof the permeate pack and a second channel entrance positioned proximateto fluid openings at the second end of the permeate pack in the array,and wherein the at least one channel opening is open through the entirethickness of the first and second retentate sheets to permit a fluid tocontact adjacent filter sheets, and wherein the first and secondretentate sheets are bonded to adjacent filter sheets about peripheralend and side portions thereof; and two assembly end plates sandwichingthe multilaminate array of sheets, each end plate having a first end anda second end corresponding to that of the multilaminate array of sheets,wherein the two assembly end plates comprise at least one fluid openingat the first end thereof and at least one fluid opening at the secondend thereof, wherein fluid openings of the end plates are in registerwith corresponding fluid openings of the permeate pack, wherein the atleast one assembly further comprises at least one permeate passageopening at longitudinal side margin portions of the sheet members of theassembly, wherein the filtration cassette further comprises a cappositioned on at least a portion of at least one fluid opening of thepermeate pack, wherein the cap is positioned proximate to channelopenings entrances of the first and second retentate sheets, and whereinthe cap has a general U-shape and transverses the permeate pack throughthe fluid opening and at least partially overlaps a first side of thefirst filter sheet and at least partially overlaps a second side of thesecond filter sheet, with the permeate sheet positioned therebetween. 2.The filtration cassette of claim 1, wherein the filtration cassette ismounted between two holder plates, wherein one holder plate comprises aport for the introduction of fluid to the filtration cassette and theother holder plate comprises a port each for the withdrawal of permeateand a port for the withdrawal of retentate from the filtration cassette.3. The filtration cassette of claim 1, wherein a temperature of a fluidintroduced to the filtration cassette is in a range from about 1° C. toabout 130° C.
 4. The filtration cassette of claim 1, wherein the capcomprises metal , ceramics, polymeric materials, or combinationsthereof.
 5. The filtration cassette of claim 1, wherein the capcomprises at least one feature to ensure a more substantial bond withthe first filter sheet and the second filter sheet.
 6. The filtrationcassette of claim 5, wherein the at least one feature: (a) includes aclip, a dimple, a hook and/or texturing; and/or (b) wherein open ends ofthe cap can extend through an opening in the permeate pack and arebonded, welded or sealed to each other to form an integral seal.
 7. Thefiltration cassette of claim 1, wherein the filtration cassette isdesigned for parallel flow of fluid within the filtration cassette andthe cap is positioned on fluid openings at the first end of the permeatepack or on both fluid openings at the first end and fluid openings atthe second end of the permeate pack.
 8. The filtration cassette of claim1, wherein the filtration cassette is designed for series flow of fluidwithin the filtration cassette and the cap is positioned on some fluidopenings at the first end of the permeate pack, or on some fluidopenings at the second end of the permeate pack, or both.
 9. Thefiltration cassette of claim 1, wherein the permeate pack furthercomprises a first permeate screen spacer positioned between the firstfilter sheet and the permeate sheet, a second permeate screen spacerpositioned between the second filter sheet and the permeate sheet, orboth, wherein each permeate screen spacer has a first end and a secondend corresponding to that of the multilaminate array of sheets whereinthe permeate screen spacers comprise at least one fluid opening at thefirst end thereof and at least one fluid opening at the second endthereof, wherein fluid openings of the permeate screen spacers are inregister with corresponding fluid openings of the permeate pack.
 10. Thefiltration cassette of claim 9, wherein the first and second permeatescreen spacers have an open area in a range from about 20% to about 80%.11. The filtration cassette of claim 1, wherein the permeate sheetcomprises stainless steel.
 12. The filtration cassette of claim 11,wherein the stainless steel is optionally indexed and diffusion bondedat wire intersections.
 13. The filtration cassette of claim 11, whereinthe filtration cassette is suitable for sonication.
 14. The filtrationcassette of claim 1, wherein the fluid openings at the first end of thearray, the fluid openings at the second end of the array, or both, arecut as an irregular pentagon having a “V” positioned proximate to thechannel entrances of the first and second retentate sheets.
 15. Thefiltration cassette of claim 14, wherein the filtration cassette isdesigned for parallel flow of fluid within the filtration cassette andthe irregular pentagons are cut at the fluid openings at the first endof the array only.
 16. The filtration cassette of claim 14, wherein thefiltration cassette is designed for series flow of liquid sourcematerial within the filtration cassette and the irregular pentagons arecut at some fluid openings at the first end and some fluid openings atthe second end of the array.
 17. The filtration cassette of claim 1,wherein a width of the permeate passage opening of the permeate sheet isless than or equal to a width of the permeate passage opening of each ofthe filter sheets and retentate sheets in the multilaminate array ofsheets.
 18. A method of separating a target substance from a liquidsource material, said method comprising: flowing the liquid sourcematerial into at least one filtration cassette of claim 1 so as torecover a permeate fluid for disposal, reuse, further filtration, or asa target product; and recovering a retentate stream for disposal, reuse,further filtration, or as a target product.
 19. The method of claim 18,wherein a temperature of the liquid source material is in a range fromabout 1° C. to about 130° C.
 20. The method of claim 18, wherein thepermeate sheet comprises stainless steel and wherein the method furthercomprises the application of an acoustic field or wave to generateultrasound waves and to enhance the separation of the target substancefrom the liquid source material.